Curse rings that gangster's put on (6)
I believe the answer is:
hoodoo
'curse' is the definition.
(thesaurus)
'rings that gangster's put on' is the wordplay.
'rings' becomes 'oo' (multiple circles).
'that gangster' becomes 'hood' (I've seen this before).
'put on' is a charade indicator (letters next to each other).
'oo' after 'hood' is 'HOODOO'.
(Other definitions for hoodoo that I've seen before include "bringer of misfortune" , "Bad luck some people bring" , "Jinx" , "Spells" , "Bringer of bad luck" .)